Simplify the following expression: $10\sqrt{99}$.
Explanation: First, try to factor a perfect square out of the radical. $= 10\sqrt{99}$ $= 10\sqrt{9 \cdot 11}$ Separate the radical and simplify. $= 10\sqrt{9} \cdot \sqrt{11}$ $= 10 \cdot 3 \cdot \sqrt{11}$ $= 30\sqrt{11}$